Wireless communication networks are well known. Some networks are completely proprietary, while others are subject to one or more standards to allow various vendors to manufacture equipment for a common system. Standards-based networks include networks, such as the Universal Mobile Telecommunications System (UMTS), the Global System for Mobile Communications (GSM) and its progeny (e.g., the General Packet Radio Service (GPRS) and the Enhanced Data rates for GSM Evolution (EDGE)), and the Long Term Evolution (LTE) system developed by the Third Generation Partnership Project (3GPP), a collaboration between groups of telecommunications associations to make globally applicable third generation (3G) mobile phone system specifications within the scope of the International Mobile Telecommunications-2000 project of the International Telecommunication Union (ITU).
The 3GPP has adopted Wideband Code Division Multiple Access (WCDMA) as the wireless air interface access for the UMTS network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. When operating over a 3G mobile telecommunications system, such as UMTS, a user can utilize a wireless communications device, such as a mobile phone, to engage in real-time video communications and conference calls, play real-time games, receive online music broadcasts, and send/receive email. However, because these functions rely on fast, instantaneous transmission, 3G systems utilize technologies, such as High Speed Packet Access (HSPA), which includes High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), to improve uplink/downlink transmission rate.
In order to improve HSDPA and HSUPA, Release 7 (R7) of the 3GPP standard provides a Continuous Packet Connectivity (CPC) protocol specification, which includes features that aim to significantly increase the number of packet data users per cell, reduce the uplink noise level resulting from such increase in packet data users, reduce power consumption at the user equipment (UE) (e.g., mobile device), and improve the achievable download capacity for various data services, such as Voice over Internet Protocol (VoIP).
According to the CPC protocol specification, discontinuous transmission (DTX) and discontinuous reception (DRX) operation is used by the UE, such as a smart phone, when transmissions between the UE and the serving base station (e.g., enhanced Node B or eNodeB) are decreasing. The DTX-DRX operation includes discontinuous uplink transmission (uplink DTX) and discontinuous downlink reception (downlink DRX). Uplink DTX is a mechanism where control signals are transmitted on the uplink control channels (e.g., the Uplink Dedicated Physical Control Channel (UL-DPCCH)) according to defined discontinuous patterns during the inactive state of corresponding uplink data channels, such as an Enhanced Dedicated Transport Channel (E-DCH) or a High Speed Physical Control Channel (HS-DPCCH), in order to maintain signal synchronization and power control loop with less control signaling. For example, uplink DTX allows the UE to align UL-DPCCH transmission with a fixed DTX pattern to maintain UE synchronization with the network. Downlink DRX is configured by a Radio Network Controller (RNC), which may form part of the serving base station, and allows the UE to restrict the downlink reception times in order to reduce power consumption. When the downlink DRX is enabled, the UE is not required to receive physical downlink channels except during pre-established time intervals.
According to prior art downlink DRX approaches in the context of CPC during HSPA data transfer, the UE receiver is activated periodically (e.g. every DRX period, which can vary from 8 to 40 milliseconds (ms)) to perform certain tasks. For example, during each active period, the UE may receive a downlink control channel, such as the High Speed Shared Control Channel (HS-SCCH), and process the received control signals to determine whether the serving base station has data to send to the UE. If the UE determines that the serving station has user data to send, the UE keeps its receiver activated so as to be able to receive the data from the serving station. After the data has been received, the UE may keep the receiver activated for an additional period of time according to an inactivity timer in case additional control information or user data is sent.
In addition to being periodically activated or awakened to monitor for data transmission notifications, the UE receiver is also typically activated during dedicated time periods to perform intra-frequency neighbor cell analysis functions so as to determine whether to select a new cell for communication. Depending on network configuration, neighbor cell analysis functions may include, among other things, detecting the presence of neighbor cells belonging to a monitored set and monitoring channel qualities of neighbor cells. The neighbor cell detection function typically occurs in multiple stages and includes receiving primary synchronization channels (stage 1), receiving secondary synchronization channels (stage 2), determining scrambling codes (stage 3), and decoding system frame numbers (SFN) (stage 4). According to 3GPP R7 Technical Specification (TS) 25.133, section 8.1.2.2.2, when DRX is active and the DRX cycle is less than ten subframes (e.g., less than 20 ms where each subframe has a 2 ms duration), the UE must identify and decode the SFN of a new cell in the monitored list within 800 ms. Alternatively, where the DRX cycle is greater than ten subframes, the UE must identify and decode the SFN of a new cell in the monitored list within 1.5 seconds.
In the context of 3GPP TS 25.133, section 8.1.2.2.2, the subframes referred to therein are generally used for monitoring the HS-SCCH of the serving cell in order to detect whether the serving base station has data to send to the UE as part of a continuing data session. Other channels, such as the Fractional Downlink Dedicated Physical Channel (F-DPCH), may also be monitored for power control purposes. To facilitate intra-frequency neighbor cell analysis, the DRX phase of CPC typically includes additional dedicated time periods which exceed the subframe duration and can extend beyond a DRX cycle (e.g., longer than 40 ms) depending on the quantity of neighbor cells to be detected and analyzed. Exemplary DTX-DRX operation is illustrated by the waveform 100 of FIG. 1. In the exemplary waveform 100, the DRX cycle between activations of the UE receiver for serving cell monitoring is 40 ms (e.g., as noted between signals 102 and 103) and the DTX cycle between activations of the UE transmitter is 320 ms (e.g., as noted between signals 105 and 106). Exemplary dedicated time periods for performing intra-frequency neighbor cell analysis are illustrated by signal waveforms 107-112, each of which is illustrated as lasting about 40 ms. While such additional dedicated time periods enable the UE receiver to perform necessary neighbor cell analysis, they also require the UE receiver to be powered on and activated, thereby utilizing valuable UE battery resources and undesirably shortening the time period between required battery recharging.
To facilitate analysis of neighbor cells other than intra-frequency neighbor cells (e.g., cells which do not operate in the same frequency band as the serving cell or operate using a different wireless protocol, such as inter-frequency neighbor cells or cells utilizing the Global System for Mobile Communications (GSM) protocol), 3GPP R7 TS 25,212 provides for a so-called “compressed mode” of operation that introduces transmission gaps in what would otherwise be allocated transmission subframes. The transmission gaps temporarily halt UE transmissions and their associated downlink power control messaging to enable the UE receiver to monitor inter-frequency or other off-frequency neighbor cells instead of power control or other control signaling from the serving cell. To be compliant with the 3GPP specification, any battery-saving solution relating to CPC should preferably be compatible with compressed mode operation.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated alone or relative to other elements to help improve the understanding of the various embodiments of the present invention.